The present invention relates to a hydraulic control valve apparatus for an automatic transmission that is installed in a vehicle.
An automatic transmission that is installed in a vehicle includes a plurality of friction engagement elements such as a clutch and a brake, and a hydraulic control apparatus that controls supply of a pressurized oil to the friction engagement elements. The friction engagement elements are selectively operated to shift between an engagement state and a disengagement state in response to the pressurized oil supplied, so that a gear ratio of the automatic transmission is determined. The hydraulic control apparatus includes a valve body formed with a hydraulic path (or a hydraulic circuit) which is connected to the respective friction engagement elements, and a shift control valve (or a hydraulic control valve) that is mounted to the valve body and operative to open and close the hydraulic path within the valve body so as to control supply a line pressure (or a hydraulic circuit pressure) to the respective friction engagement elements. The shift control valve is usually constituted of a solenoid operated valve. Specifically, the shift control valve includes a pressure regulating portion that includes a sleeve, a spool slidably moveable in the sleeve and a spring that biases the spool, and a solenoid portion including a plunger and a solenoid that electromagnetically drives the plunger. The spool has one end to which a load is applied by the plunger electromagnetically driven, and the other end to which a load is applied by the spring. The shift control valve balances the loads to thereby regulate an input pressure and produce an output pressure corresponding to an input signal, i.e., an electromagnetic force, which is applied to the solenoid portion.
In the hydraulic control apparatus as described above, the valve body may be disposed within an oil pan that is disposed below the automatic transmission. In this case, when the valve body is in an immersed state in which the valve body is immersed in oil within the oil pan, the shift control valve mounted to the valve body is kept in an immersed state in which the shift control valve is immersed in the oil. In the immersed state, a damper chamber of the shift control valve in which the spring is accommodated is always filled with the oil. On the other hand, the valve body may be disposed on a side of the automatic transmission together with the oil pan in order to provide a sufficient space below the automatic transmission and avoid interference with parts such as a drive shaft of wheels and a suspension. Japanese Patent Application First Publication No. 6-34024 indicates such an arrangement of the valve body on the side of the automatic transmission.